Hospital beds, whether of the medsurg type, stretcher type or birthing type, have heretofore been provided with castors mounted around the base for rolling the bed from place to place. At least one of the castors, and usually two, have at least two operating modes. In most cases, one of the castors will have three operating modes.
More particularly, at least one of the castors is of the type having three operating modes, known as "neutral" "brake", and "steer". In the neutral mode, the castor is free to swivel. In the brake mode, the brake castor pad is pressed against the surface of the castor wheel to prevent it from rotating and swiveling. In the steer mode, the castor is locked against swiveling movement, and aligned parallel to the longitudinal dimension of the bed so that the bed can be pushed straight down a hallway without the bed drifting to one side or the other. In two operating mode castors, the steer mode or function is eliminated, and the castor simply has neutral and brake modes.
Two types of castors, each of which includes the capability of having the above three operating modes, have been employed in hospital beds. The simplest type is known as a "plunger" type castor. In this type of castor, the castor spindle is spring loaded upwardly and normally maintains the castor locked in the steer mode. Depressing the spindle through a first displacement frees the castor from its steer mode and places it into its free-to-swivel neutral mode. Depressing the spindle through a second displacement places the castor in its brake mode by forcing the castor brake against the castor wheel thereby stopping castor wheel rotation and swiveling movement.
A more expensive castor which likewise includes the steer, neutral and brake modes is the "cam" type castor. In the cam type castor, there is an additional housing located above the spindle which houses a cam. The cam normally includes a hex-shaped through-bore for cooperation with a similarly hex-shaped shaft. The hex-shaped shaft is inserted through the cam hex bore, and rotation of the shaft rotates the cam, the lobes of which then move the spindle through the required displacements hence moving the castor from the steer to the neutral mode and from the neutral mode to the brake mode.
Hospital beds which have employed plunger type castors have also employed cable type actuating systems for actuating a rocker arm which in turn depresses the spindle to move the castor into its three operating modes. Such cable systems have typically been provided with a foot pedal for actuating the cable assembly. Normally, the pedal when in a centermost position corresponds to the castor being in its neutral mode; depressing the pedal in a first direction causes the cable assembly to move the castor via the rocker arm to its steer mode, and depressing the pedal in a second direction from a neutral position causes the cable assembly to move the castor via the rocker arm to the brake position. Such a cable assembly is subject to criticism, however, as these types of assemblies generally require numerous parts, thereby increasing the cost and complexity of the system. Furthermore, as the cables in these cable assemblies are prone to stretching over time, the tension in the cable must constantly be adjusted to provide for proper operation of the castors.
With respect to cam type castors, so-called direct drive or linkage mechanism systems have been employed to actuate these types of castors. In these systems, a rigid link is connected between the pedal and hex shaft for rotating the hex shaft and hence the cam of the castor. Such direct drive linkage assemblies have met with success in that there is a great reduction in the number of parts over that found in a typical cable assembly, the systems are less expensive, and the systems do not require constant cable tension adjustment. However, in many situations, such as, for example, retrofit situations, the cam type castor is not a feasible alterative to a plunger type castor as the larger, bulkier cam type castor cannot be substituted for the plunger type castor due to packaging constraints, etc., therefore ruling out the use of the larger cam type castor and its associated cam shaft.